The private equity firm founded by Republican presidential candidate Mitt Romney made use of arcane techniques in several of its Cayman Islands-based funds to avoid U.S. taxes, according to a trove of Bain Capital's private audit and finance records made public on the website Gawker today.

The audited financial statements of one of the Cayman Islands funds make note of the use of "blocker" entities, which are used to help retirement accounts and nonprofit entities avoid some taxes. Financial statements for another fund note that it "intends to conduct its operations so it will … not be subject to United States federal income or withholding tax ..."

Those details emerge on the statements of two funds in which Romney still holds a sizeable investment, according to the financial disclosure statements he filed when he announced his bid for president.

The publication of the Bain Documents on the Gawker website could rekindle debate about Romney's role at the company, and specifically about Bain's decision to domicile many of its funds in offshore locations known as tax havens.

Critics say Romney's investments in these funds offer just the latest example of how wealthy Americans can shelter their investments to limit the amount they pay in taxes.

"The only reason they structure it that way is to avoid tax," said Rebecca Wilkins, senior counsel with the group Citizens for Tax Justice. "It just confirms what everyone already believes about the tax system -- that it's rigged. That the rules are rigged to favor the well off."

Romney campaign officials did not immediately respond to questions about the newly published papers. But when ABC News first reported on Bain's Cayman Islands accounts, campaign officials said the purpose of locating offshore was to help attract money from foreign investors. The accounts provided no tax advantage to American investors like Romney. Romney, the campaign said, has paid all U.S. taxes on income derived from those investments.

"The tax consequences to the Romneys are the very same whether the fund is domiciled here or another country," a campaign official said at the time.

The issue of Romney's taxes have plagued his campaign. Just last week, a press conference set up to focus on Romney's Medicare plan turned into a back and forth about Romney's tax returns, and whether he had ever paid less than 13.9 percent.

Romney called the question "small-minded," lecturing reporters about the other issues facing American voters that he deems more important than his tax returns.

"I just have to say given the challenges that America faces -- 23 million people out of work, Iran about to become nuclear, one out of six Americans in poverty -- the fascination with taxes I paid I find to be very small minded compared to the broad issues we face," he said at the time. "But I did go back and look at my taxes and over the past 10 years I never paid less than 13 percent. I think the most recent year is 13.6 or something like that."

The admission by Romney came after he told ABC News in an interview that he wasn't sure if he'd ever paid less than 13.9 percent but said that he'd "be happy to go back and look."

Romney has so far released what is legally required of him, one complete year of tax returns from 2010 and an estimate for his 2011 returns. He filed an extension on his 2011 returns and the campaign has said they will be released in full by October.